This invention relates generally to ink jet printing, and more particularly to the evacuation of gas bubbles from ink jet ink delivery systems.
A typical ink jet printer has a pen that reciprocates over a printable surface such as a sheet of paper. The pen includes a print head having an array of numerous orifices through which droplets of ink may be expelled onto the surface to generate a desired pattern. The pen includes a body defining an ink chamber containing a supply of ink. The pen may be supplied by a detachable and replaceable ink cartridge, or via a flexible tub to a fixed supply, which also may be replaceable.
An issue of concern for these and other liquid ink printers is the unwanted introduction of air bubbles. Air or other gas may occur for various reasons. A printer may initially be manufactured and shipped to the end user with empty, air-filled chambers and conduits in which ink will normally reside, and which is displaced into an ink pen upon startup. The replacement of an ink supply cartridge may trap and introduce additional air. Ink may contain dissolved gas that generates bubbles. If gas bubbles are not evacuated or otherwise accommodated by design, they can block the flow of ink. Where such devices are subject to atmospheric temperature and pressure fluctuations, an expanding bubble may displace ink from the print head orifices, drool ink over the paper, and leaving residual dried ink that impairs print quality.
Past systems have addressed gas entrapment by warehousing the gas in tolerable areas of the ink supply system, providing adequate volume for gas expected to accumulate over the life of the device. However, these undesirably increase device size, and may be inadequate for devices expected to have a long life through many replacements of the ink supply cartridges. Degassed ink may be used to eliminate one source of gas, but it suffers the disadvantage of limiting the shelf life of the ink supply cartridges. Another approach is to provide a gas pumping system that engages in pumping of a volume from the system, but which is unable to distinguish between ink and gas, and therefore is prone to waste of ink, in addition to the complexity, size, and cost associated with such systems.
There is therefore the need for mechanisms which facilitate the removal of gas from ink delivery systems, and which do not add excessive cost or complexity to the ink delivery system.
Embodiments of the present invention provide a suction device connected to the ink supply chamber of an inkjet printer. The supply chamber and print engine have exit apertures to which a suction device is connected. A gas permeable film associated with the aperture separates the chamber from the suction device. The suction device may be a resilient spring member that occasionally is compressed during printer carriage reciprocation to maintain suction, or may be a vacuum pump. A porous element may support the film.